Did you know that 30% of cumulative CO₂ emissions are from land-use change?

If the starting point is 1750 or earlier, this share just goes up.


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Another factoid. Half of global CO₂ emissions in 1950 were from land-use change. That is not so long ago!

The declining share of land-use change in the total is not because the world ended deforestation, but coal, oil, & gas grew.

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CO₂ emissions from land-use change are incredibly uncertain. Uncertainty is 50% or more.

There are also definition issues in what is defined as anthropogenic (what is a carbon sink?).

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The good news, is that the Earth system has been able to clean up about half the CO₂ we have dumped in the atmosphere. The ocean takes up roughly 25% of our historical emissions and the land another 25%.

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More figures available here:


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More from @Peters_Glen

14 Oct

Is it time to move beyond net zero emissions & start discussing net negative emissions?

Why? To allow developing countries to reach net zero later (fairness) & help them escape poverty while still limiting warming to 1.5°C.

@aniruddh_mohan sciencedirect.com/science/articl…

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The carbon budget for 1.5°C is depleting rapidly, with a large share used by today’s developed countries.

Even if developed countries mitigate fast, the carbon space remaining for developing countries is minuscule.

(also see cicero.oslo.no/no/posts/cicer…)

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If global CO₂ emissions stay at net zero, either:
* All countries need to be net zero ~2050, or
* Rich countries have net negative emissions post-2050, allowing developing countries to emit longer post-2050.

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Read 12 tweets
8 Oct
"Instead of leaving such work to volunteers, global institutions should marshal the funding & expertise to collect crucial data, & mandate their publication"

💯agree with @_HannahRitchie. No one wants to fund the giant who's shoulders we stand on.


The approach to science is to fund big models, expensive observations, etc. All this is needed, but somehow science seems to have forgotten the importance careful curation & maintenance of data.
Science is full of projects that improve models, do model comparisons, process some satellite data, etc, & if you are lucky there might be a task that scrapes together some data to feed the models.
Read 10 tweets
7 Oct
It is a top day for a top ten day...

We often do plots of the top emitters, especially for fossil CO₂ emissions. But, what about other GHGs? Is it the same distribution of top emitters?

We need a thread for that...

(I know about per capita, so no need to @ me)

CO₂ emissions from net LUC (one bookkeeping model). These are net numbers, some countries are net sources, others net sinks.

Current LUC sources are concentrated in several developing countries (the rich countries cut their forests down long ago).


Don't over interpret the LUC numbers.

Different LUC datasets give different numbers. Here is the FAO data (from 2020). Indonesia is much less important in this dataset, Brazil dominates.

There is a lot of uncertainty at the country level, so be careful.

Read 10 tweets
22 Sep
#ClimateTwitter Direct Air Capture (DAC)

In 2011, Rob Socolow estimated that 1MtCO₂/yr DAC would require a contact structure with height 10m & length of 5km.

Is that still the case?


If I look at these pictures of Climeworks Orca via @EdgarHertwich

The height is ~3m, the length ~10m, & 4 units
Area: 120m² for 4000tCO₂/yr
Or: 30,000m² for 1MtCO₂/yr (120/4*1000)

If 10m high (Socolow), then contact structure ~3km long.

This is rather crude, but is quite similar to the original Socolow estimate. If true, this is fascinating…

If contact structure is 10m high, then 1MtCO₂/yr requires 3-5km structure

1GtCO₂/yr requires 3-5000km
5GtCO₂/yr requires 15-25,000km

Read 5 tweets
21 Sep
"Have you ever published a paper that *never* would have happened without twitter?" @dsquintana

Hmmm, certainly yes, & most of my papers are in some way influenced by Twitter, & five minutes on Twitter can generate lots of new paper ideas...


Perhaps the most (in)famous climate paper in recent times only came about because @MLiebreich provoked 90% of #ClimateTwitter with #RCP85isBollox, laying the foundation for this paper with @hausfath & myself
I met @Oliver_Geden on Twitter, & we have written several papers together (& have many ideas that are waiting some time & resources).

I suspect the trouble paper with @KevinClimate was heavily influenced by debates on Twitter science.org/doi/abs/10.112…

Read 7 tweets
16 Sep
Estimating CO₂ emissions from forests is difficult, not least because of different definitions.

CO₂ emissions come from conversion (cutting down or growing a tree).

There is also a 'sink', soaking up CO₂ we previously emitted.

What should be reported as CO₂ emissions?

It is really rather complex. The reason the 'sink' is included in emission accounting, is that it is difficult to determine what is 'anthropogenic'.

It was decided to use self-defined 'managed land' & include 'indirect' (climate) effects.


Scientific studies (eg IPCC Assessment Reports) generally consider CO₂ emissions from 'Net Conversions' as the emissions, while government reporting to the UNFCCC combines the conversions & sink (black line).

The 'sink' is not the total sink, only a part of the forest sink.

Read 6 tweets

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